The present invention relates to a method of magnetic transfer and an apparatus for magnetic transfer for magnetic transferring in a process of manufacturing magnetic discs used for hard disc devices and floppy disc devices.
As a typical magnetic disc device, there have already been commercialized presently some of hard disc drives having a surface recording density exceeding 1 Gigabit/sq-in, and rapid technological advancement is strongly in evidence as there are discussions about practical use of 20 Gigabit/sq-in within a few years.
In the technological background, what has enabled such a high recording density is dependent largely upon magneto-resistive element heads that are capable of reproducing signals in only a few xcexcm of track width with a high signal-to-noise ratio, besides improvements in the track recording density.
In addition, there have been demands for reduction in amount of flotage of a floating magnetic slider with respect to a magnetic recording medium in keeping with high recording density, as there are increasing a possibility of physical interactions that can occur between the disc and the slider for certain factors even while floating. Under such circumstances, there has been a demand for further smoothness of the recording media.
Here, tracking servo techniques of the head play an important role in order for the head to accurately scan a narrow track. In a currently available hard disc drive using such tracking servo techniques, a servo signal for tracking, an address data signal, a reproduction clock signal and the like are recorded at regular angular intervals in a round of the disc. A driving device detects and corrects a position of the head using these signals reproduced by the head at predetermined time intervals, thereby enabling the head to scan over the track accurately.
Since the above-described servo signal, the address data signal, the reproduction clock signal and the like are used as reference signals for the head to scan accurately over the track, a high positioning accuracy is required for writing them (hereinafter referred to as xe2x80x9cformattingxe2x80x9d). In the current hard disc drives, formatting is made with a special-purpose servo device (henceforth xe2x80x9cservo writerxe2x80x9d) equipped therein with a highly accurate position detecting device, which utilizes optical interference to position the recording head.
However, the following problems exist in the formatting made by the servo writer.
First, it takes a considerable time to write signals over a large number of tracks while positioning the head with a high accuracy. It is therefore necessary to operate many servo writers at the same time in order to increase productivity.
Secondly, it costs a large amount of money to provide a large number of the servo writers and to maintain them. These problems become more serious the more the number of tracks increases as a track density improves.
Hence, there has been proposed a method in that a disc called master disc, on which a complete servo data is written in advance, is overlapped with a magnetic disc to be formatted, and the data on the master disc is transferred into the magnetic disc in batch by externally impressing energy for the magnetic transfer, thus formatting is performed instead of using a servo writer.
A magnetic transfer apparatus described in Japanese Patent Laid-Open Publication, No. H10-40544, is now cited as an example.
The above publication discloses a method including the steps of forming a magnetic area composed of ferromagnetic material in a shape of a pattern corresponding to data signals on a surface of a substrate to prepare a master disc for magnetic transfer, making the surface of the master disc for magnetic transfer to be in contact with a surface of a magnetic recording medium of either a sheet-form or a disc-form whereon either a ferromagnetic thin film or a coated layer of ferromagnetic powder is formed, and recording on a magnetic recording medium a magnetized pattern in a shape of the pattern corresponding to the data signals formed on the master disc for magnetic transfer by applying a magnetic field of a predetermined magnitude.
However, since there is normally a clearance of approximately 30 nm between the head and a surface of the disc when the disc is in rotation, it is therefore necessary to keep unevenness on the surface of the disc within a maximum of approximately 20 nm. The magnetic head may come in contact with the magnetic recording medium during recording and reproducing the data, if any bumps larger than the above exist on the magnetic recording medium. In such a case, a space between the magnetic head and the magnetic disc increases at the instant of contact, and causes performance of recording and reproducing signals to decrease. It has also been a cause of shortening a useful life of the magnetic head, as the magnetic head makes physical contact with the magnetic disc.
In other words, although the magnetic transfer apparatus disclosed in Japanese Patent Laid-Open Publication, No. H10-40544, can complete the formatting instantly, it requires a strict surface control, on the other hand, in order to ensure practical use with the foregoing clearance between the head and the disc, since the master disc for magnetic transfer and the magnetic disc come in contact over the entire surfaces.
In addition, disc-shaped recording media such as magnetic discs, magneto-optical discs, optical discs and the like are advancing toward higher performance such as downsizing, thinning, increased capacity and so on in recent years, and demands for higher density recording media have been rising in keeping pace with the advancement as described above. Disc-shaped recording media having high accuracy and high reliability are necessary in order to meet such demands, therefore making it an urgent need to manufacture disc-shaped recording media with outstanding flatness and smoothness, and without adhesion of fine particle, etc. during recording of data.
On the contrary, it is difficult for the above-described magnetic transfer apparatus of the prior art to avoid fine foreign particles from getting into it, even if very strict control is carried out. Such foreign particles have caused small anomalous unevenness on a surface of the master disc or the magnetic disc at a moment the master disc and the magnetic disc to be formatted are overlapped together. Silicon is used generally as material of the master disc. If the magnetic disc is made of a material of lower hardness than that, such as aluminum for example, bumps of foreign particles on the master disc are transferred in shape as dimples on the magnetic disc side, and if on the other hand the magnetic disc is made of a material of higher hardness such as glass for example, foreign particles located on the magnetic disc produce defects on the master disc side.
In the above case, the defects are reproduced on all of magnetic discs to which magnetic transfer is performed, thereby making it difficult to manufacture the magnetic discs of high quality efficiently and steadily.
Accordingly, the present invention is intended to realize a magnetic transfer apparatus that is capable of accurate magnetic transfer in order to manufacture magnetic discs of high quality by decreasing size of such small bumps to a level not to cause the problems, and to prevent errors in recording and reproducing.
A method of magnetic transfer of the present invention is a manufacturing method including the steps of closely contacting a master disc for magnetic transfer, whereon a magnetic film is formed, with a surface of a magnetic disc, whereon a ferromagnetic layer is formed, and magnetically transferring a pattern of the magnetic film on the master disc for magnetic transfer onto the surface of the magnetic disc using an external magnetic field, wherein the magnetic transfer is carried out by mounting the regular magnetic disc only after repeating suctioning and forced feeding of gas between the master disc for magnetic transfer and a dummy disc, when making the master disc for magnetic transfer to contact forcibly by using the dummy disc first. Taking this method can maintain a surface of the master disc for magnetic transfer in a smooth condition free from foreign particles and burrs at all the time during magnetic transferring, thereby realizing manufacture of magnetic discs of high quality, as there occurs practically no fine bump to cause problems, as far as the magnetic discs subject to the magnetic transfer are concerned.
Also, the method of magnetic transfer of the present invention further includes defect detection means for detecting defects on a surface of a magnetic disc. When this defect detection means detects defects in number equal to or greater than a predetermined number on the surface of the magnetic disc, the magnetic transferring is carried out by placing it in close contact with a master disc for magnetic transfer, only after repeating an operation of contacting and separating the master disc for magnetic transfer with a dummy disc for a predetermined number of times, and replacing the dummy disc by the magnetic disc not subjected to the magnetic transfer. The above step helps to provide the method of magnetic transfer capable of ensuring the magnetic transferring of high quality into magnetic discs for a long period of time, since it allows a regular maintenance of removing dust and foreign particles on the master disc for magnetic transfer.
Furthermore, in the present invention, a region on the master disc for magnetic transfer where contacting with and separating from the dummy disc is so arranged as to completely cover a magnetic transfer region from the master disc for magnetic transfer to the magnetic disc during magnetic transfer. This realizes manufacture of magnetic discs of high quality, as servo signals are accurately transferred even on a rim in a peripheral area of the magnetic disc.
Moreover, the method of magnetic transfer of the present invention is to carry out the magnetic transfer by placing the master disc for magnetic transfer in close contact with a magnetic disc, only after repeating an operation of contacting and separating a dummy master disc with the magnetic disc for a predetermined number of times, and replacing the dummy master disc by the master disc for magnetic transfer. This method is able to remove foreign particles on the magnetic disc, thereby realizing an accurate magnetic transfer while assuring a remarkably smooth surface and high reliability.
Furthermore, an apparatus for magnetic transfer of the present invention is to make a master disc for magnetic transfer, whereon a magnetic film is formed on at least one of surfaces thereof, in close contact with a magnetic disc, and to magnetically transfer a pattern of the magnetic film on the master disc for magnetic transfer onto the magnetic disc by applying an external magnetic field. The apparatus for magnetic transfer includes the master disc for magnetic transfer whereon a predetermined data to be transferred is written, a retainer slidably positioned on a guide member for retaining the master disc for magnetic transfer, a support base provided with a vent hole for supporting the magnetic disc or a dummy disc, a feeding unit for supplying gas into the vent hole provided in the support base, an exhaust unit for evacuating gas through the vent hole, and a magnet for applying magnetic field for the magnetic transfer. The foregoing structure is able to maintain a surface of the master disc for magnetic transfer in a smooth condition free from foreign particles and burrs at all the time during magnetic transferring, thereby realizing manufacture of magnetic discs of high quality as practically no small bump occurs on the magnetic discs subject to the magnetic transfer.